Transmitter architecture employing space time spreading and orthogonal transmit diversity techniques

ABSTRACT

Disclosed is a common transmitter architecture having incorporated both open loop transmit diversity schemes using a plurality of binary switches. Employment of binary switches allows for the sharing of certain components whether the transmitter is utilizing a orthogonal transmit diversity (OTD) scheme or a space time spreading (STS) scheme. Accordingly, the number of components in the transmitter is minimized and the complexity of the transmitter is simple enough to be implemented into a single application specific integrated chip.

RELATED APPLICATION

Related subject matter is disclosed in the following application andassigned to the same assignee hereof: U.S. patent application Ser. No.09/294,661 entitled, “Method And Apparatus For Downlink Diversity InCDMA Using Walsh Codes,” inventors R. Michael Buehrer, Robert AtmaramSoni, and Jiann-an Tsai, filed on Apr. 19, 1999. Related subject matteris disclosed in the following concurrently filed application andassigned to the same assignee hereof: U.S. patent application Ser. No.09/395,325 entitled, “A Receiver Architecture Employing Space TimeSpreading And Orthogonal Transmit Diversity Techniques,” inventors R.Michael Buehrer, Robert Atmaram Soni and Stephen A. Allpress.

FIELD OF THE INVENTION

The present invention relates generally to wireless communicationsystems and, in particular, to wireless communication employing transmitdiversity.

BACKGROUND OF THE RELATED ART

Several third generation wireless communication systems are beingdeveloped. One such third generation wireless communication system isknown as CDMA 2000. In CDMA 2000, a variety of techniques are beingincorporated for improving call quality. Open loop transmit diversity isone such technique in which user signals are transmitted using twoantennas. In a first phase of CDMA 2000, open loop transmit diversity iscurrently being implemented in a form of orthogonal transmit diversity(OTD). In OTD, separate antennas are used to transmit even data bits andodd data bits to achieve transmit diversity and improved call quality.

In a second phase of CDMA 2000, open loop transmit diversity may beimplemented in a form of space time spreading (STS) using Walshfunctions or codes. STS enhances call quality by providing variable gainover OTD depending on the coding rate being used. Specifically, in STS,odd data bits and even data bits are jointly, not separately,transmitted over two antennas. However, the manner in which the odd andeven data bits are modulated/processed before being transmitted over oneantenna will be different from the manner in which the odd and even databits are modulated/processed being transmitted over the other antenna.

There has been some concern that including both open loop transmitdiversity schemes as options in CDMA 2000 would be very complex in termsof implementing them into a common transmitter architecture.Accordingly, there exists a need for a simple way to implement commontransmitter architecture that has incorporated orthogonal transmitdiversity and space time spreading schemes.

SUMMARY OF THE INVENTION

The present invention is a common transmitter architecture havingincorporated both open loop transmit diversity schemes using a pluralityof binary switches. Employment of binary switches allows for the sharingof certain components whether the transmitter is utilizing a orthogonaltransmit diversity (OTD) scheme or a space time spreading (STS) scheme.Accordingly, the number of components in the transmitter is minimizedand the complexity of the transmitter is simple enough to be implementedinto a single application specific integrated chip.

The transmitter has an OTD and a STS mode, and comprises a first andsecond antenna system. The first antenna system comprises timemultiplexers, mixers, switches and adders. The time multiplexers areused to time multiplex an in-phase first signal with a second in-phasefirst signal to produce a first time multiplexed signal; a quadraturephase first signal with a second quadrature phase first signal toproduce a second time multiplexed signal; an in-phase second signal withan inverted in-phase second signal to produce a third time multiplexedsignal; and a quadrature phase second signal with an inverted quadraturephase second signal to produce a fourth time multiplexed signal. Themixers are used to mix outputs of the time multiplexers with a Walshfunction to produce first, second, third and fourth mixed timemultiplexed signals. The first and second time multiplexed signals aredirected to the adders. If the transmitter is in STS mode, the switchesdirect the third and fourth mixed time multiplexed signals to the addersso they may be added with the first and second mixed time multiplexedsignals, respectively. If the transmitter is in OTD mode, the switchesdo not direct the third and fourth mixed time multiplexed signals to theadders.

The second antenna system comprises time multiplexers, mixers, switchesand adders. The time multiplexers are used to time multiplex an in-phasesecond signal with an inverted in-phase second signal when thetransmitter is in the first operating mode and with an in-phase secondsignal when the transmitter is in the second operating mode to produce afifth time multiplexed signal; a quadrature phase second signal with aninverted quadrature phase second signal when the transmitter is in thefirst operating mode and with a quadrature phase second signal when thetransmitter is in the second operating mode to produce a sixth timemultiplexed signal; an in-phase first signal with an inverted in-phasefirst signal to produce a seventh time multiplexed signal; and aquadrature phase first signal with an inverted quadrature phase firstsignal to produce an eighth time multiplexed signal. The mixers are usedto mix outputs of the time multiplexers with a Walsh function to producefifth, sixth, seventh and eighth mixed time multiplexed signals. Thefifth and sixth time multiplexed signals are directed to the adders. Ifthe transmitter is in STS mode, the switches direct the seventh andeighth mixed time multiplexed signals to the adders so they may be addedwith the fifth and sixth mixed time multiplexed signals, respectively.If the transmitter is in OTD mode, the switches do not direct theseventh and eighth mixed time multiplexed signals to the adders.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, aspects and advantages of the present invention willbecome better understood with regard to the following description,appended claims, and accompanying drawings where:

FIG. 1 depicts a transmitter employing orthogonal transmit diversity andspace time spreading using Walsh functions in accordance with thepresent invention; and

FIG. 2 depicts one finger of a receiver employing orthogonal transmitdiversity and space time spreading using Walsh functions in accordancewith the present invention.

DETAILED DESCRIPTION

FIG. 1 depicts a common transmitter architecture 10 in accordance withthe present invention. Transmitter 10 is typically incorporated at abase station, and is operable to modulate/process user signals employingeither orthogonal transmit diversity or space time spreading (usingWalsh or some other orthogonal function) techniques. Transmitter 10comprises of a first antenna system 11 and a second antenna system 28.For ease of discussion, the present invention will be described hereinwith respect to one user signal. It should be understood, however, thatthe present invention can be applied to multiple user signals.

Transmitter 10 receives a user signal Y. Before user signal ismodulated/processed by first and/or second antenna systems 11 and 28,user signal Y is parsed and partitioned into even and odd data bits andthen into in-phase and quadrature phase signals, i.e. signal Y isconverted into signals Y_(I1), Y_(Q1), Y_(I2), and Y_(Q2), wherein Irepresents an in-phase signal, Q represents a quadrature phase signal, 1represents even data bits and 2 represents odd data bits. SignalsY_(I1), Y_(Q1), Y_(I2), and Y_(Q2) are provided as inputs to first andsecond antenna systems 11 and 28.

First antenna system 11 comprises time multiplexers 12, inverters 14,switches 16 and 26, amplifiers 18 and 20, mixers 22 and adders 24.Switches 16 and 26 have a first position and second position. Whenswitches 16 and 26 are all in the first position, first antenna system11 operates in orthogonal transmit diversity mode. By contrast, whenswitches 16 and 26 are all in the second position, first antenna system11 operates in space time spreading mode.

User signal Y_(I1) is provided twice as input to time multiplexer 12-1.The output of time multiplexer 12-1 is a time multiplexed signal ofsignal Y_(I1) with itself. When switch 16-1 is in the first position,i.e., OTD mode, the output of time multiplexer 12-1 is directed toamplifier 18-1 where it is amplified a gain G by amplifier 18-1. Whenswitch 16-1 is in the second position, i.e., STS mode, the output oftime multiplexer 12-1 is directed to amplifier 20-1 where it isamplified a gain $\frac{G}{\sqrt{2}}$

by amplifier 20-1.

The outputs of amplifier 18-1 and amplifier 20-1 are mixed at mixer 22-1with a Walsh function W₁, and then provided as input to adder 24-1. Notethat mixer 22-1 should only receive an input from either amplifier 18-1or 20-1 at any one time, and that some other orthogonal (orquasi-orthogonal) function may be used to mix the output of amplifier18-1 and 20-1 instead of Walsh functions. If first antenna system 11 isin STS mode, i.e., switches 16 and 26 are all in the second position,the output of mixer 22-1 is added to an output of mixer 22-3 by adder24-1 before being transmitted. By contrast, if first antenna system 11is in OTD mode, i.e., switches 16 and 26 are all in the first position,the output of mixer 22-1 is not added to the output of mixer 22-3 byadder 24-1 before being transmitted.

User signal Y_(QI) is processed in a similar manner as user signalY_(I1) using time multiplexer 12-2, switch 16-2, amplifiers 18-2 and20-2, mixer 22-2, adder 24-2 and Walsh function W₁.

User signal Y_(I2) is provided as input to time multiplexer 12-3 alongwith an inverted signal of Y_(I2) (i.e. output of inverter 14-1). Theoutput of the time multiplexer 12-3 is then provided as input toamplifier 20-3, where it is amplified a gain $\frac{G}{\sqrt{2}}.$

The output of amplifier 20-3 is mixed with a Walsh function W₂ by mixer22-3. When switch 26-1 is in the second position, the output of mixer22-3 is provided as input to adder 24-1 where it can be added to theoutput of mixer 22-1. By contrast, when switch 26-1 is in the firstposition, the output of mixer 22-3 is not provided as input to adder24-1.

Note that the amplifiers used by first antenna system 11 has a gain of$\frac{G}{\sqrt{2}}$

when it is in STS mode and a gain of G when it is in OTD mode. Suchconfiguration allows for a same output power by first antenna system 11regardless of the mode. But it should be understood that anyconfiguration of amplifiers and gains may be used. Further note thatwhen first antenna system 11 is in OTD mode, it transmits only even databits. By contrast, when first antenna system 11 is in STS mode, ittransmits both even and odd data bits.

User signal Y_(Q2) is processed in a similar manner as signal Y_(I2)using time multiplexer 12-4, inverter 14-2, amplifier 20-4, mixer 22-4,switch 26-2, adder 24-2 and Walsh function W₂.

Second antenna system 28 comprises switches 29, 33 and 40, inverters 30,time multiplexers 32, amplifiers 34 and 36, mixers 38 and adders 42.Switches 29, 33 and 40 have a first and second position. When switches29, 33 and 40 are in the first position, second antenna system 28operates in OTD mode. By contrast, when switches 29, 33, and 40 are inthe second position, second antenna system 28 operates in STS mode.

When switch 29-1 is in the first position, user signal Y_(I2) isprovided as input to time multiplexer 32-1 along with an inverted usersignal Y_(I2) (i.e., output of inverter 30-1). When switch 29-1 is inthe second position, user signal Y_(I2) is provided twice as input totime multiplexer 32-1. In time multiplexer 32-1, user signal Y_(I2) istime multiplexed with itself or its inverted self depending on theposition of switch 29-1 (or mode of second antenna system 28).

When switch 33-1 is in the first position, the output of timemultiplexer 32-1 is directed to amplifier 34-1, where the timemultiplexed signal is amplified a gain G by amplifier 34-1. When switch33-1 is in the second position, the output of time multiplexer 32-1 isdirected to amplifier 36-1, where the time multiplexed signal isamplified a gain $\frac{G}{\sqrt{2}}$

by amplifier 36-1.

The outputs of amplifiers 34-1 and 36-1 are provided as input to mixer38-1, where they are mixed with Walsh functions W₃. Note that mixer 38-1should only receive an input from either amplifier 34-1 or 36-1 at anyone time, not both simultaneously. If second antenna system 28 is in STSmode, i.e., switches 29, 33 and 40 are all in the second position, theoutput of mixer 38-1 is added to an output of mixer 38-3 by adder 42-1before being transmitted. By contrast, if second antenna system 28 is inOTD mode, i.e., switches 29, 33 and 40 are all in the first position,the output of mixer 38-1 is not added to the output of mixer 38-3 byadder 42-1 before being transmitted.

User signal Y_(Q2) is processed in a similar manner to user signalY_(I2) using switches 29-2, 33-2 and 40-2, inverter 30-2, timemultiplexer 32-2, amplifiers 34-2 and 36-2, mixer 38-2, adder 42-2 andWalsh function W₃.

User signal Y_(I1) is provided as input to time multiplexer 32-3 alongwith an inverted user signal Y_(I2). In time multiplexer 32-3, usersignal Y_(I1) is time multiplexed with its inverted self. The output oftime multiplexer 32-3 is amplified a gain $\frac{G}{\sqrt{2}}$

by amplifier 36-3.

The output of amplifier 36-3 is mixed in mixer 38-3 with Walsh functionW₄. When switch 40-1 is in the second position, the output of mixer 38-3is provided as input to adder 42-1 where it is added to the output ofmixer 38-1. When switch 40-1 is in the first position, the output ofmixer 38-3 is not provided as input to adder 42-1.

User signal Y_(QI) is processed in a similar manner to user signalY_(I1) using inverter 30-4, time multiplexer 32-4, amplifier 36-4, mixer38-4, switch 40-2 and adder 42-2.

Note that, like the amplifiers of first antenna system 11, theamplifiers of second antenna system 28 has a gain of$\frac{G}{\sqrt{2}}$

when it is in STS mode and a gain of G when it is in OTD mode. Suchconfiguration allows for a same output power by second antenna system 11regardless of the mode. But it should be understood that anyconfiguration of amplifiers and gains may be used. Further note thatwhen second antenna system 28 is in OTD mode, it transmits only odd databits. By contrast, when second antenna system 28 is in STS mode, ittransmits both even and odd data bits.

In a preferred embodiment, Walsh functions W₁, W₂, W₃ and W₄ areidentical. Note that for ease of discussion, a common receiverarchitecture is disclosed herein that assumes that Walsh functions W₁,W₂, W₃ and W₄ are identical. It should be understood that the differentWalsh functions W₁, W₂, W₃ and W₄ or combinations thereof may also beused, and that the common receiver architecture disclosed herein couldbe adapted for different Walsh functions W₁, W₂, W₃ and W₄ orcombinations thereof.

Opposite of transmitter 10 is a receiver (typically incorporated at amobile-station) for receiving and demodulating/processing the signalstransmitted by transmitter 10. FIG. 2 depicts one finger 50 of a commonreceiver architecture in accordance with the present invention. Finger50 being operable to demodulate/process received signals (transmitted bytransmitter 10 or equivalent) employing either orthogonal transmitdiversity or space time spreading (using Walsh or some other orthogonalfunction) techniques. Finger 50 comprises mixers 52, 54, 56, 58, 60 and62, adders 64, 66, 68 and 70, time multiplexer 72, inverters 59, 61 and63, integrators 53 and 55 and switches 74, 76 and 78. Switches 74, 76and 78 have a first and a second position. When switches 74, 76 and 78are all in the first position, finger 50 operates in OTD mode. Bycontrast, when switches 74, 76 and 78 are all in the second position,finger 50 operates in STS mode.

When finger 50 receives a signal r(t), received signal r(t) is providedas inputs to mixers 52 and 54. In mixer 52, received signal r(t) ismixed with an extended Walsh function w(t), i.e., repeated Walshfunction w(t). The output of mixer 52 is provided as input to integrator53. In mixer 54, received signal r(t) is mixed with a function{overscore (w)}(t), which is a complement of the extended Walsh functionw(t). The output of mixer 54 is provided as input to integrator 55.Recall that for ease of discussion, it is assumed that Walsh functionsW₁, W₂, W₃ and W₄ are identical at transmitter 10. Accordingly, Walshfunction w(t) is identical to Walsh functions W₁, W₂, W₃ and W₄.

In integrators 53 and 55, the outputs of mixers 52 and 54 are integratedover the length of the Walsh functions w(t) or {overscore (w)}(t) (orsymbol rate) and then dumped. Note that the mixers 52 and 54 mixes at achip rate. The output of integrator 53 is provided as inputs to mixers56 and 62. The output of integrator 55 is provided as input to mixer 58,and a conjugate of the output of mixer 54 is provided as input to mixer60, wherein the conjugate of the output of mixer 54 is obtained byinverting a quadrature stream of the output of mixer 54 using inverter61.

In mixer 56, the output of mixer 52 is mixed with a signal ĥ₁*representing a conjugate of a channel estimate for first antenna system11. In mixer 62, the output of mixer 52 is mixed with a signal ĥ₂*representing a conjugate of a channel estimate for second antenna system28. In mixer 58, the output of mixer 54 is mixed with the signal ĥ₂*. Inmixer 60, the conjugate of the output of mixer 54 is mixed with a signalĥ₁ representing a channel estimate for first antenna system 11. Notethat, in one embodiment, the channel estimates for first and secondantenna systems 11 and 28 are obtained using pilot signals transmittedfrom first and second antenna systems 11 and 28, respectively.

The output of mixer 56 is provided as input to adder 64. When switch 74is in the second position, a conjugate of the output of mixer 58 is alsoprovided as input to adder 64 where the conjugate of the output ofmixers 58 and the output of mixer 56 are added together. Note that theconjugate of the output of mixer 58 is obtained by inverting aquadrature stream of the output of mixer 58 using inverter 59. Theoutput of adder 64 is provided as input to adder 68, where it is addedwith outputs of same relative mixers from other fingers.

When switch 74 is in the first position, the output of mixer 58 isprovided as input to adder 66. When switches 76 and 78 are in the secondposition, an inverted output of mixer 60 (via inverter 63) and theoutput of mixer 62 are provided as inputs to adder 66. When switches 76and 78 are in the first position, the inverted output of mixer 60 andthe output of mixers 62 are not provided as inputs to adder 66. Notethat the output mixer 58 should not be provided as input to adder 66 atthe same time as the inverted output of mixer 60 and output of mixer 62.The output of adder 66 is provided as input to adder 70, where it isadded with outputs of same relative mixers from other fingers.

The outputs of adders 68 and 70 are time multiplexed with each other bytime multiplexer 72 and directed to a decoder, not shown. Note that ineither mode, output of mixer 64 corresponds to a received version of theeven data bits and the output of mixer 66 corresponds to a receivedversion of the odd data bits.

The present invention is described herein with reference to certainembodiments, such as wireless communication systems based on thirdgeneration code division multiple access techniques. It should beunderstood that the present invention may be applicable to wirelesscommunications based on other multiple access techniques. Additionally,instead of even and odd data bits for a same user signal, the presentinvention may be applied to even and odd data bits for different usersignals or some other combinations. The present invention may also beapplied to two identical non-partitioned (into odd and even data bits)user signals. Accordingly, the present invention should not be limitedto the embodiments disclosed herein.

We claim:
 1. A transmitter comprising: a first time multiplexer for timemultiplexing an in-phase first signal with a second in-phase firstsignal; a first mixer for mixing an output of the first time multiplexerwith a first function; a second time multiplexer for time multiplexing aquadrature phase first signal with a second quadrature phase firstsignal; a second mixer for mixing an output of the second timemultiplexer with the first function; a third time multiplexer for timemultiplexing an in-phase second signal with an inverted in-phase secondsignal; a third mixer for mixing an output of the third time multiplexerwith a second function; a fourth time multiplexer for time multiplexinga quadrature phase second signal with an inverted quadrature phasesecond signal; a fourth mixer for mixing an output of the fourth timemultiplexer with the second function; a first switch having a first andsecond position for directing an output of the third mixer; a secondswitch having a first and second position for directing an output of thefourth mixer; a first adder for adding an output of the first mixer andthe output of the third mixer when the first switch is in the secondposition and not when the first switch is in the first position; and asecond adder for adding an output of the second mixer and the output ofthe fourth mixer when the second switch is in the second position andnot when the second switch is in the first position.
 2. The transmitterof claim 1, wherein the first and second functions are orthogonal orquasi-orthogonal functions.
 3. The transmitter of claim 1, wherein thefirst and second functions are Walsh functions.
 4. The transmitter ofclaim 1, wherein the first and second functions are different.
 5. Thetransmitter of claim 1, wherein the first and second functions areidentical.
 6. The transmitter of claim 1 further comprising: a firstamplifier for amplifying the output of the first time multiplexer; asecond amplifier for amplifying the output of the second timemultiplexer; a third amplifier for amplifying the output of the thirdtime multiplexer; and a fourth amplifier for amplifying the output ofthe fourth time multiplexer.
 7. The transmitter of claim 6, wherein thethird amplifier amplifies the output of the third time multiplexer by again $\frac{G}{\sqrt{2}},$

the fourth amplifier amplifies the output of the fourth time multiplexerby a gain $\frac{G}{\sqrt{2}},$

the first amplifier comprises a first amplifier A for amplifying theoutput of the first time multiplexer by a gain G and a first amplifier Bfor amplifying the output of the first time multiplexer by a gain$\frac{G}{\sqrt{2}},$

and the second amplifier comprises a second amplifier A for amplifyingthe output of the second time multiplexer by a gain G and a secondamplifier B for amplifying the output of the second time multiplexer bya gain $\frac{G}{\sqrt{2}}.$


8. The transmitter of claim 7, wherein the transmitter is in a firstoperating mode when the first and second switches are in the firstposition and in a second operating mode when the first and secondswitches are in the second position, the transmitter further comprising:a third switch for directing the output of the first time multiplexer tothe first amplifier A when the transmitter is in the first operatingmode and to the first amplifier B when the transmitter is in the secondoperating mode; and a fourth switch for directing the output of thesecond time multiplexer to the second amplifier A when the transmitteris in the first operating mode and to the second amplifier B when thetransmitter is in the second operating mode.
 9. The transmitter of claim1, wherein the in-phase and quadrature phase first signals comprise evendata bits of a user signal and the in-phase and quadrature phase secondsignals comprise odd data bits of the user signal.
 10. The transmitterof claim 1, wherein the in-phase and quadrature phase first signals andthe in-phase and quadrature phase second signals are identical signals.11. The transmitter of claim 1, wherein the in-phase and quadraturephase first signals and the in-phase and quadrature phase second signalsare different signals.
 12. The transmitter of claim 1 wherein thetransmitter is in a first operating mode when the first and secondswitches are in the first position and in a second operating mode whenthe first and second switches are in the second position, thetransmitter further comprising: a fifth time multiplexer for timemultiplexing a second in-phase second signal with a second invertedin-phase second signal when the transmitter is in the first operatingmode and with a third in-phase second signal when the transmitter is inthe second operating mode; a fifth mixer for mixing an output of thefifth time multiplexer with a third function; a sixth time multiplexerfor time multiplexing a second quadrature phase second signal with asecond inverted quadrature phase second signal when the transmitter isin the first operating mode and with a third quadrature phase secondsignal when the transmitter is in the second operating mode; a sixthmixer for mixing an output of the sixth time multiplexer with the thirdfunction; a seventh time multiplexer for time multiplexing a thirdin-phase first signal with an inverted in-phase first signal; a seventhmixer for mixing an output of the seventh time multiplexer with a fourthfunction; an eighth time multiplexer for time multiplexing a thirdquadrature phase first signal with an inverted quadrature phase firstsignal; an eighth mixer for mixing an output of the eighth timemultiplexer with the fourth function; a third adder for adding an outputof the fifth mixer and an output of the seventh mixer when thetransmitter is in the second operating mode; and a fourth adder foradding an output of the sixth mixer and an output of the eighth mixerwhen the transmitter is in the second operating mode.
 13. Thetransmitter of claim 12 further comprising: a third switch having afirst and second position, wherein the output of the seventh mixer isdirected to the third adder when the third switch is in the secondposition and not directed to the third adder when the third switch is inthe first position; and a fourth switch having a first and secondposition, wherein the output of the eighth mixer is directed to thefourth adder when the fourth switch is in the second position and notdirected to the fourth adder when the fourth switch is in the firstposition.
 14. The transmitter of claim 12, wherein the first and secondfunctions are orthogonal or quasi-orthogonal functions.
 15. Thetransmitter of claim 12 further comprising: a first inverter forinverting the third in-phase second signal to produce the secondinverted in-phase second signal; a second inverter for inverting thethird quadrature phase second signal to produce the second invertedquadrature phase second signal; a third switch having a first and secondposition, wherein the third in-phase second signal is directed to thefifth time multiplexer when the third switch is in the second positionand directed to the first inverter when the third switch is in the firstposition; and a fourth switch having a first and second position,wherein the third quadrature phase second signal is directed to thesixth time multiplexer when the fourth switch is in the second positionand directed to the second inverter when the fourth switch is in thefirst position.
 16. The transmitter of claim 12 further comprising: afirst amplifier for amplifying the output of the fifth multiplexer; asecond amplifier for amplifying the output of the sixth timemultiplexer; a third amplifier for amplifying the output of the seventhtime multiplexer; and a fourth amplifier for amplifying the output ofthe eighth time multiplexer.
 17. The transmitter of claim 16, whereinthe third amplifier amplifies the output of the seventh time multiplexerby a gain $\frac{G}{\sqrt{2}},$

the fourth amplifier amplifies the output of the eighth time multiplexerby a gain $\frac{G}{\sqrt{2}},$

the first amplifier comprises a first amplifier A for amplifying theoutput of the fifth time multiplexer by a gain G and a first amplifier Bfor amplifying the output of the fifth time multiplexer by a gain$\frac{G}{\sqrt{2}},$

and the second amplifier comprises a second amplifier A for amplifyingthe output of the sixth time multiplexer by a gain G and a secondamplifier B for amplifying the output of the sixth time multiplexer by again $\frac{G}{\sqrt{2}}.$


18. The transmitter of claim 17 further comprising: a first switch fordirecting the output of the fifth time multiplexer to the firstamplifier A when the transmitter is in the first operating mode and tothe first amplifier B when the transmitter is in the second operatingmode; and a second switch for directing the output of the sixth timemultiplexer to the second amplifier A when the transmitter is in thefirst operating mode and to the second amplifier B when the transmitteris in the second operating mode.
 19. A transmitter having a first and asecond operating mode comprising: a first time multiplexer for timemultiplexing an in-phase first signal with an inverted in-phase firstsignal when the transmitter is in the first operating mode and with asecond in-phase first signal when the transmitter is in the secondoperating mode; a first mixer for mixing an output of the first timemultiplexer with a first function; a second time multiplexer for timemultiplexing a quadrature phase first signal with an inverted quadraturephase first signal when the transmitter is in the first operating modeand with a second quadrature phase first signal when the transmitter isin the second operating mode; a second mixer for mixing an output of thesecond time multiplexer with the first function; a third timemultiplexer for time multiplexing an in-phase second signal with aninverted in-phase second signal; a third mixer for mixing an output ofthe third time multiplexer with a second function; a fourth timemultiplexer for time multiplexing a quadrature phase second signal withan inverted quadrature phase second signal; a fourth mixer for mixing anoutput of the fourth time multiplexer with the second function; a firstswitch having a first and second position for directing an output of thethird mixer; a second switch having a first and second position fordirecting an output of the fourth mixer; a first adder for adding anoutput of the first mixer and the output of the third mixer when thefirst switch is in the second position and not when the first switch isin the first position; and a second adder for adding an output of thesecond mixer and the output of the fourth mixer when the second switchis in the second position and not when the second switch is in the firstposition.
 20. The transmitter of claim 19, wherein the first and secondfunctions are orthogonal or quasi-orthogonal functions.
 21. Thetransmitter of claim 19, wherein the first and second functions areWalsh functions.
 22. The transmitter of claim 19, wherein the first andsecond functions are different.
 23. The transmitter of claim 19, whereinthe first and second functions are identical.
 24. The transmitter ofclaim 19 further comprising: a first inverter for inverting the secondin-phase first signal to produce the inverted in-phase first signal; asecond inverter for inverting the second quadrature phase first signalto produce the inverted quadrature phase first signal; a third inverterfor inverting a second in-phase second signal to produce the invertedin-phase second signal; a fourth inverter for inverting a secondquadrature second signal to produce the inverted quadrature secondsignal; a third switch having a first and second position for directingthe second in-phase first signal, wherein the second in-phase firstsignal is directed to the first time multiplexer when the third switchis in the second position and directed to the first inverter when thethird switch is in the first position; and a fourth switch having afirst and second position for directing the second quadrature phasefirst signal, wherein the second quadrature phase first signal isdirected to the second time multiplexer when the fourth switch is in thesecond position and directed to the second inverter when the fourthswitch is in the first position.
 25. The transmitter of claim 19 furthercomprising: a first amplifier for amplifying the output of the firstmultiplexer; a second amplifier for amplifying the output of the secondtime multiplexer; a third amplifier for amplifying the output of thethird time multiplexer; and a fourth amplifier for amplifying the outputof the fourth time multiplexer.
 26. The transmitter of claim 25, whereinthe third amplifier amplifies the output of the third time multiplexerby a gain $\frac{G}{\sqrt{2}},$

the fourth amplifier amplifies the output of the fourth time multiplexerby a gain $\frac{G}{\sqrt{2}},$

the first amplifier comprises a first amplifier A for amplifying theoutput of the first time multiplexer by a gain G and a first amplifier Bfor amplifying the output of the first time multiplexer by a gain$\frac{G}{\sqrt{2}},$

and the second amplifier comprises a second amplifier A for amplifyingthe output of the second time multiplexer by a gain G and a secondamplifier B for amplifying the output of the second time multiplexer bya gain $\frac{G}{\sqrt{2}}.$


27. The transmitter of claim 26 further comprising: a third switch fordirecting the output of the first time multiplexer to the firstamplifier A when the transmitter is in the first operating mode and tothe first amplifier B when the transmitter is in the second operatingmode; and a fourth switch for directing the output of the second timemultiplexer to the second amplifier A when the transmitter is in thefirst operating mode and to the second amplifier B when the transmitteris in the second operating mode.
 28. The transmitter of claim 19,wherein the in-phase and quadrature phase first signals comprise evendata bits of a user signal and the in-phase and quadrature phase secondsignals comprise odd data bits of the user signal.
 29. The transmitterof claim 19, wherein the in-phase and quadrature phase first signals andthe in-phase and quadrature phase second signals are identical signals.30. The transmitter of claim 19, wherein the in-phase and quadraturephase first signals and the in-phase and quadrature phase second signalsare different signals.